I am going to work off my poor memory here, Robert. If I remember correctly the purpose of the tow bar was to hook two jeeps together to form a prime mover for towed artillery like a 105mm? Someone correct me if I'm wrong.
The USMC had a field book that showed a typical Division had approximately 400 jeeps, 250 1 ton, & 250 2-1/2 ton trucks.
The photos I have seen show the 75mm pack howitzers being towed by the 1 ton IHC M-2-4 and the 105 and 155mm towed by IHC open cab 2-1/2 ton trucks.
It is possible the Army, which on a lot of PTO island invasions used artillery, had jeeps with tow bars but I have not seen any photos of such in the PTO.
MB-NAVY-MZ-1 352625 - 07/20/44 (DOD est.)